Thermally stable esters



United States Patent 3,290,357 THERMALLY STABLE ESTERS Marvin M. Fein, 14 Woodbrook Circle, Westfield, N.J., and Nelson N. Schwartz, 9 Darrah Lane E., Trenton,

Nb brawin Filed Nov. 13, 1963, S91. No. 324,172 11 Claims. (Cl. 260487) This invention relates to novel halogenated esters of carboranes heretofore unreported in the literature.

More particularly this invention concerns the preparation of the trihaloacetate esters of hydroxylterminated carboranes such as the monoand bis-hydroxylalkyl carboranes and certain of their derivatives. These esters are thermally stable, high density compositions having utility as components of explosive mixtures as well as in fluids used for heat transfer and dielectric applications.

The novel esters of this invention have the formula:

wherein X is a halogen, R is an alkylene radical, and R is selected from the group consisting of hydrogen and in the last formula R and X having the meaning ascribed to them above.

The symbol ivHio alternatively referred to as 0 (theta) represents the carbor'ane group.

While there is no paucity of solid high explosives, there is a need for high explosives which are liquid at ambient temperatures. Particularly valuable explosive components in the liquid form would be those which are relatively insensitive to detonation prior to compounding yet, when mixed with the proper activating materials would produce a liquid explosive having a high brissance. This type of liquid explosive would have value in several types of commercial and military applications where solid explosives cannot effectively be used. For example, in mining and quarrying operations, there is frequently a need to implant a high explosive charge in narrow crevices, cracks or fissures where no solid charge could be inserted without markedly enlarging the opening. The enlargement of these openings is not only time-consuming and expensive, but it increases the possibility of accidental landslides and cave-ins. For these mining applications liquid state explosives would be most useful.

Similarly, liquid explosive mixtures would be especially suitable for tactical military operations. For example, in guerrilla or partisan warfare a liquid explosive mixture which could be carried inconspicuously in bottles or other non-metallic containers would be most useful. Since the liquid components of the explosive mixture are metal-free and could be stored in non-metallic containers, detection by presently used electronic means Would be virtually impossible. In addition, unlike solid form explosives, those explosives would not require bulky or intricate detonating devices since when they are mixed with certain materials they become exceedingly sensitive to detonation by shock and will auto-detonate within a short time. An example of this type of liquid explosive is given infra. Since few liquid components of liquid high explosive mixtures are available which are shock insensitive prior to formulation and form highly detonation sensitive high explosives after formulation, the preparation of the novel carborane esters is a significant advance in the art.

3,290,357 Patented Dec. 6, 1966 Thus it is an object of this invention among many others to prepare novel liquid esters which are useful as components of high explosive mixtures.

It is another object of this invention to prepare the above esters which form high explosive mixtures having high sensitivity toward detonation by shock, yet prior to formulation are relatively shock insensitive.

It is a further object of this invention to prepare thermally stable, heat transfer fluids having good dielectric properties.

Further objects of this invention will become apparent to those skilled in the art after a perusal of the remaining X CC0GCX R2CCR1OH II II 101110 X,O( JOH R -C-C-R 0(fiCX;

ioHm wherein X is a halogen, R is an alkylene radical, and R is selected from the group consisting of hydrogen and in the last formula R and X having the meaning previously ascribed tothem.

Examples of the many trihaloacetoxyalkyl carboranes which can be prepared by the inventive process are the bisesters such as:

l,2-bis(trifluoroacetoxymethyl) carborane, 1,2-bis (trifiuoroacetoxyethyl) carborane, 1,2-bis (trifluoroacetoxyisopropyl) carborane, 1,2-bis (trifiuoroacetoxypropyl) carborane, the 1,2-bis (trifluoroacetoxybutyl) carboranes, the 1,2-bis (trifluoroacet-oxypentyl) carboranes, the 1,2- bis (trifluoroacetoxyhexyl) carboranes, the 1,2-bis (trifluoroacetoxyheptyl) carboranes. Among the corresponding bis trichloro esters are included 1,2-bis (trichloroacetoxymethyl) carborane, 1,2-bis (trichloroacetoxyethyl)carborane, the 1,2-bis (trichloroacetoxypropyl)carboranes, the 1,2-bis (trichloroacetoxybutyl)carboranes, the 1,2-bis (trichloroacetoxyphentyl) carboranes, the 1,2- bis (trichloroacetoxyhexyl) carboranes, the l,2-bis (trichloroacetoxyheptyl) carboranes, and the 1,2-bis (trichloroacetoxyoctyl) carboranes as well as the corresponding 1,2 bis tribromino and triodoacetoxyalkyl carborane esters. Among the l-mono esters which can be prepared are:

1-trifiuoroacetoxymethylcarborane, 1-trifluoroacetoxyethylcarborane,

the 1 trifiuoroacetoxypropylcarbzoranes,

the 1-trifluoroacetoxybutylcarboranes,

the 1-trifluoroacetoxypentylcarboranes,

the 1-trifluoroacet-oxyhexylcarboranes,

the 1-trifluoroacetoxyheptylcarboranes, and the 1-trifiuoroacetoxyoctylcarboranes.

'Also included are the corresponding mono trichloro esters such as 1-trichloroacetoxymethylcarborane, esters such as trichloroacetoxymethylcarborane, the 1-trichloroacetoxypropylcarboranes,

the 1-trichloroacetoxybutylcarboranes,

the 1-trichloroacetoxypentylcarboranes, the 1-trichloroacetoxyhexylcarboranes,

the 1-trichloroacetoxyheptylcarboranes, and the 1-trichloroacetoxyoctylcarboranes as well as the corresponding mono-l-tribromoand triodiacetoxyalkylcarborane esters.

Conveniently the mono or bis hydr-oxyalkylcarborane is contacted with at least a stoichiometric amount of a source of the trihaloacetoxy radical under esterifying conditions, i.e., heat and anhydrous conditions, until a substantial quantity of the l-mono or 1,2-bis (trihaloacetoxyalkyl) carborane ester is formed. The ester can be both isolated and purified by distillation or any other means used in the isolation or purification of esters.

The novel products of this invention can be prepared using various modifications of the described esterification reaction without substantially deviating from the inventive concept. For example, the order of adding the reactants is unimportant and reaction conditions such as temperature and pressure need not be rigidly controlled. For instance, the temperature at which esterification takes place can range between 30 and 200 C. Since the low er temperature range appreciably extends reaction time and the upper temperature range introduces competing side reactions, the process is run between about 50 and 120 C. This narrower temperature range gives optimum yields and is for this reason preferred. Smaller batches of product can be prepared conveniently using a steam bath as the heating source. Again while the esterification can be operated under a wide range of pressure conditions ranging from sub-through superatmospheric pressures, no advantage arises in using pressures substantially below or above atmospheric pressure. For this reason near atmospheric pressures are preferred. Since the reaction times are dependent upon the reaction conditions as well as the particular reactants used, they cannot be stated with precision except that ordinarily the reaction is substantially complete within 24 hours and seldom would extend beyond 48 hours.

As indicated earlier the trihaloacetoxy group can be contributed by a. variety of sources. Preferably the trihaloacetic acid anhydrides are used as the esterifying reactants. These reactants are preferred because they are commercially available inexpensive products which rapidly esterify the monoor bis-hydroxyalkylcarboranes. However in the alternative it is possible to employ the trihaloacetic acids as reactants under esterification conditions well defined in organic chemistry. In the alternative method, the usual esterification catalysts can be used.

These include among others, hydrogen chloride, concentrated sulfuric acid or boron trifluoride. Yet another alternative source of the trihaloacetate group are the trihaloacetyl halides such as trifluoroacetyl chloride or trichloroacetyl chloride. However, these reactants are less preferred since they are somewhat tedious to prepare and are not all available commercially.

The preferred trihaloacetoxy reactants, trifluoroacetic anhydride and trichloroacetic anhydride, are commercially available products or can be prepared directly from the anhydrous acids by distillation with a dehydrating agent. Satisfactory dehydrating agents include phosphorous pentoxide, acetic anhydride, acetyl chloride, among others. The trihaloacetic acids are common chemicals of commerce. The trihaloacetyl halide reactants can be made from the acid by distilling the anhydrous acid with thionyl chloride, phosphorous oxychloride or the like.

The 1,2-bis hydroxyalkylcarborane reactants of this invention may be prepared by the interaction of the diacetate ester of the appropriate acetylenic diol and 6,9-bis (acetonitrile) decaborane to yield the 1,2-bis (acetoxyalkyl) carborane. This intermediate is then hydrolysed in either aqueous acid or base to yield the 1,2-bis (hydroxyalkyl) carborane. For example, the lowest member of the series, 1,2-bis hydroxymethyl) carborane, is prepared by reacting 1,4-diacetoxy-2-butyne with 6,9-bis (acetonitrile) decaborane until the 1,2-bis (acetoxymethyl) carborane is prepared in substantial amount and then transesterifying with alcoholic hydrogen chloride to 1,2-bis (hydroxymethyl) carborane.

The l-hydroxyakylcarborane reactants are prepared similarly by contacting the monoacetate esters of the appropriate acetylenic monohydric alcohol with 6,9-(bisacetonitrile) decarborane to yield the l-acetoxyalkyl) carborane and hydrolysing in aqueous acid or base to form the l-hydroxyalkyl-carborane. For example, the lowest member of the series, l-hydroxymethyl carborane, can be prepared by reacting 1,4-diacetoxy-2-butyne with bis (acetonitrile) decarborane and hydrolysing the intermediate to the l-hydroxymethyl-carborane.

The amounts of the two reactants will, of course, be dependent upon whether the mono ester or the bis (di) ester is being prepared. In the case of the former product, at least a 1:1 mole ratio of the two reactants is desirable with a larger excess not being harmful. However, a large excess of the hydroxyl containing reactant is to be avoided since yields are diminished. Similarly, where the bisesters are to be prepared since there are two available hydroxyl groups, at least two moles of trihaloacetate reactant is desirable, with a large excess of the reactant being preferred. Obviously where less than two moles of the trihaloacetate reactant are used for each mole of the hydroxyalkylcarborane, the yields are reduced and a mixture of the monoand diester are produced.

In one embodiment of this invention, the 1,2-bis (hydroxymethyl) carborane, trichlor-oacetate ester is prepared by refluxing 20 parts by weight of 1,2-bis (hydroxymethyl) carborane, 35 parts by weight of trichloroacetic acid, 250 parts by weight of toluene and 1 part by weight of concentrated sulfuric acid for 4 hours, and during this time the water is stripped off in the form of its toluene azeotrope. The pressure is further reduced to 1 mm. and the byproducts distilled off at about C. The residue oil boils at 220 C./ 0.1 mm. and is shown by its infrared spectra to be the desired ester product.

In another invention embodiment, the l-hydroxypropylcarborane, trichloroacetate ester is prepared by refluxing 20 parts by weight of the trichloroacetyl chloride, 17 parts by weight of 1-hydroxypropylcarborane, 1 part by weight of sulfuric acid and 250 parts by weightof toluene for 16 hours. Again the product is stripped to a thick oil under vacuum and identified by infrared. The oil boiled at 170 C./.05 mm.

Another embodiment of this invention concerns the preparation of the 1-hydroxyisopropylcarborane, trichloroacetate ester by refluxing a composition consisting of 10 parts by weight of 1-hydroxyisopropylcarborane, 18 parts by weight trichloroacetyl chloride, 100 parts by weight of toluene for a period of 5 hours. The excess water is removed by azeotropic distillation and the reaction byproducts are removed by vacuum distillation. Infrared analysis establishes the identity of the product which boils at C./0.1 mm.

Further embodiments of this invention are as follows:

The tribromoacetate ester of 1,2-bis (hydroxybutyl) carborane is prepared by refluxing for 6 hours a reaction mixture comprising 70 parts by weight of tribromoacetyl chloride, 30 parts by weight of 1,2-bis (hydroxybutyl) carborane, 200 parts by weight of toluene and 2 parts by weight of concentrated sulfuric acid. After removing the water and by-products as described previously. Infrared analysis of the residue indicated the presence of the desired ester.

The 1,2-bis (hydroxyethyl) carborane, trichloroacetate ester is prepared by refluxing a composition consisting of 10 parts by weight of 1,2-bis (hydroxye'thyl) carborane, 30 parts by weight of trichloroacetyl chloride, 100 parts by weight of toluene for a period of 7 hours. The excess water is removed by azeotropic distillation and the re- 5. action by-produc'ts are removed by vacuum distillation. Infrared analysis establishes the identity of the product.

The trichloroacetate ester 1,2-bis (hydroxypropyl) carborane is prepared by refluxing a reaction mixture comprising 55 parts by weight 1,2-bis (hydroxypropyl) carborane, 90 parts by weight of trichloroacetyl chloride, 500 parts by weight of toluene and 1 part by weight of concentrated sulfuric acid. During 14 hours of refluxing the water is azeotropically distilled oif and the by-products removed under a high vacuum. The residual product was a very high boiling oil whose identity was confirmed by infra-red analysis.

The tribromoacetate ester of 1,2-bis (hydroxybutyl) carborane is prepared by refluxing 56 parts by weight of 1,2-bis (hydroxybutyl) carborane, 115 parts by weight of trichloroacetyl chloride, 300 parts by weight of toluene and 1 part by weight of concentrated sulfuric acid for 48 hours. During this time, the water is removed by distilling oil the toluene azeotrope and finally the byproducts stripped oif under high vacuum. The residue was a brownish oil Whose identity was confirmed by infrared analysis.

The tribr-omoacetate ester of 1,2-bis (hydroxypentyl) carborane is prepared by refluxing for 6 hours, a reaction mixture comprising 90 parts by weight of tribromoacetyl chloride, 30 parts by weight of 1,2-bis (hydroxypentyl) carborane, 200 parts by weight of toluene and 2 parts by weight of concentrated sulfuric acid. After removing the water and by-products as described previously. Infrared analysis of the high boiling oil residue indicated the presence of the desired ester.

The mono and his trihaloacetate esters of this inven tion are advantageous in a number of respects. For example, all of the esters of this invention possess the unusual combination of thermal stability, chemical inertness which gives them utility as heat transfer fluids in pressurized cooling and heating systems. In addition, in some instances the esters can be combined with nitrated substances such as nitrogen tetroxide to prepare highly explosive mixtures. However, as in any large group of COmpOundS, some members within the group are preferred for some reasons to the group as a whole. In the case of the trihaloacetate ester products of this invention, the compounds having alkylene radicals (R) of 6 or less carbon atoms are favored since they are less costly and tedious to prepare and the intermediates for their preparation are more readily available.

While several uses and advantages of the ester products of this invention have been disclosed, others will become L apparent to the reader after further reading of this application.

It is to be clearly pointed out that the foregoing embodiments and examples are illustrative only and do not constitute the metes and bounds of this invention. Numerous changes in reactants and reaction conditions can be made without departing from the invention concept.

Example ].Preparati0n of 1,2-bis (trifluoroacetoxymethyl) carborane (A) Preparation of 1,2-bis (acetoxymetltyl) carb0rane.-A mixture of 1000 parts by weight of bis (acetonitrile) decaborane and 758 parts by weight of 1,4 diacetoxy-2-butyne are dissolved in 7760 parts by weight of toluene and the solution heated to a temperature of 6098 C. for 7.6 hours. The reaction product is cooled to room temperature and filtered. The filtrate is mixed with 1760 parts by weight of methanol and heated to convert the non-carborane constitutents of the mixture to borates, after which the methyl borate and excess methanol are removed by distillation.

The distillation residue is extracted with 4686 parts by weight of boiling n-hexane to extract the 1,2-bis (acetoxymethyl) carborane. The extract is chilled to -20 C. at which point the above carborane precipitates.

An 856 parts by weight portion of dried product is obtained.

(B) Preparation of 1,2-bis (lzydroxym'ethyl carb0rane).A solution of 674 parts by weight portion of the intermediate of Part A is dissolved in 700 parts by weight of anhydrous methanol and the solution is heated for 4 hours in the presence of anhydrous hydrogen chloride. The reaction by-product, methyl acetate, is removed by distillation as a methyl acetate-methanol azeotrope. The residue, 1,2-bis (hydroxymethyl) carborane, is recrystallized from toluene and yields 470 parts by weight of crystalline material.

(C) Preparation of ester pr0duct.A 10 parts by weight portion of the bis-hydrox'ymethyl material from Part B is treated with 32 parts by weight of trifluoroacetic anhydride by refluxing for lhour. The resultant solution is fractionally distilled to yield 15 parts by weight of the trifluoroacetate of 1,2-bis (hydroxymethyl) carborane. Infra-red analysis confirmed the identity of the product.

Example 2.Preparati0n of 1-triflu0r0acet0xymethyl carborane (A) Preparation of l-acetoxymethyl carb0rane.A mixture of 202 parts by weight of his (acetonitrile) decaborane, 98 parts by weight of proparagyl acetate and 400 parts by weight of toluene are heated at reflux for 24 hours. The intermediate is recovered after converting the non-carborane portion to methyl borate by extracting twice with 400 parts by weight of n-hexane, and chilling the combined n-hexane extracts to 20 C. The 1- acetoxymethylcarborane precipitates out in substantially quantitative yield.

(B) Preparation of I-lzydroxymethyl carb0rane.Us ing the preparation and isolation procedure described in Example 1, Part B, a 108 parts by weight portion of the l-acetoxymethylcarborane is converted to the l-hydroxymethylcarborane by heating a methanol solution of the compound in the presence of anhydrous hydrogen chloride.

(C) Preparation of est-er product-A 10 parts by weight portion of the l-hydroxymethylcarb-orane of Part B is suspended in 16 parts by weight of trifluoroacetic anhydride on the steam bath for 1 hour. At the end of this time the reaction mixture is fractionally distilled to give 11 parts by weight of 1-trifluoroacetoxymethylcarborane product. Infra-red analysis confirms the identity.

Example 3.-Preparati0n 0f 1,2-bis (lzydroxyethyl) carborane trifluoroacetate ester Using the preparation and isolation procedure described in Example 1, Part B, a reaction mixture comprising 1 part by weight of concentrated sulfuric acid, 35 parts by weight portion of trifluoroacetic acid, 180 parts by weight portion of toluene and 20 parts by weight portion of 1,2-bis (hydroxyethyl) carborane is refluxed for 36 hours, during which time the water is azeotropically removed. The solvents and volatile reactants are stripped oif under vacuum. The residual oil ester product had a boiling point of C. at 0.01 mm. Infra-red and elemental analysis confirmed the identity of the product.

Example 4.Preparati0n of 1-lriclzl0r0acetoxymethyl carborane, trichloroacetate ester Using the preparation and isolation procedure described in Example 1, Part B, a reaction mixture comprising 1 part by weight of concentrated sulfuric acid, 17 parts by weight of l-hydroxymethyl carborane, and 20 parts by weight of trichloroacetic acid are refluxed for 36 hours. After the azeotropic distillation and vacuum stripping, an ester in the form of an oil boiling at C. 0.05 mm. is obtained.

Example 5.-Preparati0n of 1,2-bis (ltydroxybutyl) carborane trifluoroacetate ester Using the preparation and isolation procedure described in Example 1, Part B, a reaction mixture comprising 1 part by weight of concentrated sulfuric acid, 35 parts by weight portion of trifluoroacetic acid, 180 parts by weight portion of toluene and 10 parts by weight portion of 1,2-bis (hydroxybutyl) carborane is refluxed for 36 hours, during which time the water is azeotropically removed. The solvents and volatile reactants are stripped off under vacuum. The residual ester product was a high boiling oil. Infra-red and elemental analysis confirmed the identity of the product.

Example 6.Utility example showing the preparation of an explosive mixture of a representative ester of this invention and tetranitromethane (A) Preparation of 1,2-bis (hydroxymethyl) carborane, triflaoroacetate ester.-A 10 parts by weight portion of 1,2-bis (hydroxymethyl) ca-rborane derived from the acid hydrolysis of the reaction product of 1,4-diacetoxy-2- butyne and 6,9-bis (acetonitrilo) decaborane, is refluxed for 1 hour with 52 parts by weight of trifluoroacetic anhydride. The resultant solution is distilled to yield parts by weight of the trifluoroacetate ester.

(B) Preparation of the explosive reaction mixture. The explosive reaction mixture is prepared by mixing 23.8 parts by weight of the above ester with 60.8 parts by weight of tetranitrornethane using a stream of nitrogen gas to bring about a homogeneous solution. After detonation a plate dent depth value of 0.142" is obtained. A standard sample of TNT detonated under the same condition gives a dent depth of 0.119".

The stoichiometry is believed as shown below, balanced to produce CO It is to be clearly pointed out that the foregoing embodiments are illustrative only and do not constitute the metes and bounds of this invention. Numerous changes in reactants and reaction conditions can be made without departing from the inventive concept.

We claim:

1. Novel thermally stable esters of the formula:

wherein X is a halogen, R is a lower alkylene radical, and R is selected from the group consisting of hydrogen and 8 2. The esters of claim 1 wherein R is hydrogen and X is fluorine.

3. The esters of claim 1 wherein R is 

1. NOVEL THERMALLY STABLE ESTERS OF THE FORMULA: 